GTK+ minimum version

[Jasper Huijsmans]

OK,

With the recent addition of the systray code to libgui we now depend on
gtk 2.2 functions. I don't know exactly, but the fact is we do.

We have to make a decission if we really want to keep gtk 2.0
compatibility. If we do we either have to provide alternatives for the
gtk 2.2 functions used or only conditionally compile systray related
functions.

Benny, can you estimate how hard it would be to not depend on gtk 2.2
functions?

	Jasper